Loading ramp adapted to bridge a pair of platforms

ABSTRACT

A loading ramp is disclosed which is adapted to bridge the distance between a fixed platform, such as a loading platform, and a vertically movable platform, such as the floor of a railroad car, spaced therefrom. The ramp has a stepped undersurface at one end adapted to engage the edge of the movable platform, while the other end of the ramp is being supported upon the fixed platform. The upper surface of the end of the ramp adapted to engage the movable platform is substantially flush thereto. Housings are mounted on both sides of the ramp and each opens toward the end of the ramp that is adapted to be supported on the fixed platform. A plurality of arms are pivotally connected at one end of the housing for pivotal movement about a common horizontal axis extending substantially transversely of the ramp. At least two of the arms vary in overall length and extend out of the open end of the housing. The pivotal movement of the arms is limited by engagement of the arms with upper and lower surfaces of the housing. Each arm has at its free end a plurality of downwardly extending teeth adapted to extend below the undersurface of the ramp when the arms pivot downwardly into engagement with the lower surface of the housing. A resilient generally cylindrical member is disposed in the housing between the point of connection of the arms to the housing and the rear wall thereof with its longitudinal axis being spaced from and substantially parallel to the horizontal axis of the arms. The arms have cut-out portions encircling at least a portion of the periphery of the resilient members and contact the resilient member on the periphery thereof.

United States Patent [191 Christensen 51 May 6,1975

Carl 0. Christensen, Alamo, Calif.

[73] Assignee: Roll-Rite Corporation, Oakland,

Calif.

[22] Filed: Mar. 2, 1973 [21] Appl. No.: 337,633

[75] Inventor:

[52] US. Cl. 14/72 [51] Int. Cl ..E01d 15/12 [58] Field of Search 14/72, 71

[56] References Cited UNITED STATES PATENTS 686,490 11/1901 Uphoff 14/72 1,137,645 4/1915 McCormickl... 14/72 1,384,114 7/1921 Arnold 14/72 2,337,138 12/1943 Van Berg 14/72 3,238,548 3/1966 Christensen.... 14/72 3,491,394 l/l970 Le Clear 14/72 3,553,757 l/l97l Noland 14/72 Primary Examiner-Nile C. Byers, Jr. Attorney, Agent, or FirmPhillips, Moore, Weissenberger, Lempio & Strabala [57] ABSTRACT A loading ramp is disclosed which is adapted to bridge the distance between a fixed platform, such as a loading platform, and a vertically movable platform, such as the floor of a railroad car, spaced therefrom. The ramp has a stepped undersurface at one end adapted to engage the edge of the movable platform, while the other end of the ramp is being supported upon the fixed platform. The upper surface of the end of the ramp adapted to engage the movable platform is substantially flush thereto. Housings are mounted on both sides of the ramp and each opens toward the end of the ramp that is adapted to be supported on the fixed platform. A plurality of arms are pivotally connected at one end of the housing for pivotal movement about a common horizontal axis extending substantially transversely of the ramp. At least two of the arms vary in overall length and extend out of the open end of the housing. The pivotal movement of the arms is limited by engagement of the arms with upper and lower surfaces of the housing. Each arm has at its free end a plurality of downwardly extending teeth adapted to extend below the undersurface of the ramp when the arms pivot downwardly into engagement with the lower surface of the housing. A resilient generally cylindrical member is disposed in the housing between the point of connection of the arms to the housing and the rear wall thereof with its longitudinal axis being spaced from and substantially parallel to the horizontal axis of the arms. The arms have cut-out portions encircling at least a portion of the periphery of the resilient members and contact the resilient member on the periphery thereof.

11 Claims, 8 Drawing Figures PATENTEU HAY 81975 SHEEI 2 BF 2 LOADING RAMP ADAPTED TO BRIDGE A PAIR OF PLATFORMS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to loading ramps and more particularly to a loading ramp for bridging the distance between a fixed and a movable platform that may be locked in position although the effective bridging distance between the platforms may vary to some degree.

2. Description of the Prior Art In US. Pat. No. 3,238,548, l disclosed a self-locking ramp which is adapted to bridge the space between a pair of platforms, one being fixed and the other being movable. The ramp included a plurality of locking arms pivoted within a common housing that limited or restricted the movement of each arm and wherein the arms and housing as a unit was selectively mounted to the side of the ramp to cover a specified range of spacing distances between two such platforms.

However, although such a ramp effectively carried out what was intended, in certain instances problems arose. For example, the ramp is generally used to load railroad cars or the like adjacent a fixed loading platform. Initially, as in FIG. 2 of my aforementioned patent, the inner upper surface of the ramp at the railroad car is generally flush with the floor of the car. However, as the car is loaded with goods or the like, the weight of the goods brings the planar surface of the floor of the car down to an angle which is dangerously steep with respect to the planar surface of the ramp. At this point, a V-shaped channel or the like is formed at the junction of the ramp to the car. The passage thereover of a fork lift truck or the like for loading the car becomes increasingly hazardous and accidents have occurred. Further, the ramp of my aforementioned patent extended into the interior of the railroad car (i.e., onto a substantial portion of the movable platform) a short distance in order to provide a smooth flush transition from the planar surface of the ramp to that of the railroad car. This distance, albeit short, utilized space which could be better used for loading.

Also, when a lift a ck passes over the ramp to enter into the car with II\ it ad, the shifting weight sometimes sways the car and cases the fixed platform end of the 'ramp to bounce up before the rear wheels of the truck pass onto the ramp. The pivotal arms of the ramp move out of engagement with the fixed platform and lock in the next tighter position with a toggle action. This causes the fixed platform end of the ramp to jam or lock in a dangerous up position. Thus, the rear wheels of the truck may hit the upwardly extending edge of the ramp causing serious accidents.

Further, as the railroad car is loaded, it may move downwardly to a point where the ramp is jammed between the platforms. If a fork lift truck moves onto the ramp at this time, something might give, i.e., by breaking off sections of either the fixed platform, the railroad car or the ramp. Even if nothing gives, it is extremely difficult and dangerous to pull loose such jammed ramps.

Finally, although the arms on the ramp of my aforementioned patent served to lock the ramp in position, the ramp was still subject to a certain amount of lateral shift due to the lack of any suitable biasing means for the arms.

SUMMARY OF THE INVENTION It is an object of this invention to provide a loading ramp for bridging the space between a fixed and a movable platform in a manner whereby the ramp does not extend onto the movable platform, yet its upper surface is maintained generally flush with the upper surface of the movable platform.

It is a further object of this invention to provide such a ramp that eliminates any gap between it and the movable platform while its upper surface is maintained flush with the upper surface of the movable platform.

It is a still further object of this invention to resiliently bias such a ramp in a fixed, stable non-gap forming position between the platforms.

These and other objects are preferably accomplished by providing a ramp having a stepped undersurface at one end adapted to engage the edge of the movable platform while the other end of the ramp is being supported upon the fixed platform. The upper surface of the end of the ramp adapted to engage the movable platform is substantially flush thereto. Housings are mounted on both sides of the ramp and each opens toward the end of the ramp that is adapted to be supported on the fixed platform. A plurality of arms are pivotally connected at one end of the housing for pivotal movement about a common horizontal axis extending substantially transversely of the ramp. At least two of the arms vary in overall length and extend out of the open end of the housing. The pivotal movement of the arms are limited by engagement of the arms with upper and lower surfaces of the housing. Each arm has at its free end a plurality of downwardly extending teeth adapted to extend below the undersurface of the ramp when the arms pivot downwardly into engagement with the lower surface of the housing. A resilient generally cylindrical member is disposed in the housing between the point of connection of the arms to the housing and the rear wall thereof with its longitudinal axis being spaced from and substantially parallel to the horizontal axis of the arms. The arms have cut-out portions encircling the periphery of the resilient member and engaging at least a portion of the periphery of the resilient member.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an isometric view of the ramp of my invention in locking position between a pair of platforms;

FIG. 2 is a side elevational view of the ramp of FIG.

FIG. 3 is a side elevational view similar to the view of FIG. 1 with portions thereof removed for convenience of illustration;

FIGS. 4 and 5 are plan views of portions of the ramp of FIGS. 1 through 3;

FIGS. 6 and 7 are side views of a portion of the ramp of FIG. 3 taken through the center thereof; and

FIG. 8 is a perspective view of the resilient cylinder.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, FIG. 1 shows a bridging ramp 10, supported at one end upon a fixed platform 11, such as a loading dock, and at the other end by the bed or movable platform 12' of a vehicle body 12, such as a railroad car or the like. Bridging ramp 10 comprises a body portion 13 formed with a stepped undersurface 14 that engages a shoulder 15 of platform 12. The surface engagement between ramp l and shoulder l5 limits movement of the ramp in the direction toward platform 12, but does not prevent or limit either vertical lifting of ramp or movement thereof in the direction toward platform 11.

This invention is more particularly directed to that ramp structure and a combination of apparatus which limits movement of the ramp, especially in the direction toward platform 11, for various bridging distances between platforms 11 and 12. For this purpose there is provided at least a pair of arms 16 and 16a (see also FIG. 2) which are mounted to ramp l0 and provide contact surfaces engageable with a common vertical abutment 17 of platform 12. Each arm is pivoted from one end upon a common pivot shaft 18, the other end being formed with a plurality of downwardly extending teeth 19 that are adapted to make surface contact with abutment 17 for a limited range of spacing distances between platforms 11 and 12. These teeth 19 may be tapered downwardly as shown, if desired. In addition, a housing 20 is provided for arms 16 and 16a, the housing having upper and lower surfaces and 26 (see particularly FIG. 3) which limit or restrict the pivotal movement of each arm. Housing 20, as shown in FIG. 3, also includes rear wall 27. Such a housing 20 and arms 16 and 16a may be mounted on both sides of ramp body 13 as individual units to cover a given range of distances between platforms 1 l and 12 with an average selected distance of intended use. Thus, the same unitary assembly of arms 16 and 16a and housing 20 may be used with various lengths of ramps, or the assembly may be located on ramps of identical length as to accomodate an essentially different range of platform spacing.

It will be noted that ramp 10 is further provided with a pair of U-shaped brackets 21. These brackets may be respectively engaged by the fork of a forklift truck, which may be used either for setting the ramp in place or removing the same from a bridging position. Each bracket 21 is pivoted upon a common horizontal axis below the upper supporting surface of the ramp, and the brackets may be pivoted into vertical positions, as shown, from positions within U-shaped recesses 22 and 23, respectively.

At this point, the essential differences between the ramp of my aforementioned patent and the ramp presented herein will now be discussed. As can be seen in FIGS. 1 through 3, the edge of ramp 10 at platform 12 no longer extends into platform 12. The upper surface of platform 12 is substantially flush with the upper surface of body portion 13 of ramp l0 and no gap exists between the ramp l0 and platform 12. Preferably, ramp 10 includes a pair of supporting members 28 which do extend from ramp 10 into vehicle 13 but in a manner taking up extremely little space (see particularly FIG. 1). These members serve to maintain the upper surface or body portion 13 of ramp l0 flush with platform 12.

Further, the individual arms of my aforementioned patent have been replaced by at least a pair of the arms 16 and 16a, each arm having a plurality of the teeth 19 thereon (i.e., each arm is one integral unit having a plurality of teeth). Thus, the distances between pivot shaft 18 and the outer edges of each of teeth 19 vary, as clearly shown in FIG. 2.

Referring now to FIG. 3, the arms 16 and 16a and their relationship with ramp 10 and housing 20 are shown in detail. A pair of generally horizontal slots 29 are formed in arms 16 and 16a, respectively. Pivot shaft 18 (see also FIGS. 1 and 2) passes through slots 29. In this manner, arms 16 and 16a pivot thereabout as illustrated in FIG. 3. Slots 29 include offset portions 30 for reasons to be discussed further hereinbelow (see also FIGS. 4 and 5). The arms 16 and 16a thus extend out of housing 20 as shown and are prevented from upward movement by wall 25 of housing 20 and from downward movement by wall 26. The housings 20 are preferably welded on both sides of ramp 10 with their upper walls generally flush with body portion 13 (that is, the welds are flush with the top of the side walls of ramp 10). In this manner, side wall 32 of housing 20 (FIGS. 1 and 2) and the side rails 33 of ramp l0 serve to retain arms 16 and 16a within housing 20 and prevent lateral movement thereof.

An elongated aperture 34 is preferably formed in at least one of the side rails 33 of ramp 10 for receiving the fork (not shown) of a conventional forklift truck. In this manner, the entire ramp 10 can be quickly and easily picked up lengthwise and moved to a second location along loading platform 11 (this, of course, in addition to being able to pick ramp 10 up crosswise by brackets 21).

As discussed heretofore, it is desired to resiliently bias arms 16 and 16a in a plurality of self-locking positions between platforms 11 and 12. This is preferably accomplished by providing a resilient member such as a generally cylindrical rubber member as cylinder 35 within housing 20 rearwardly of arms 16 and 16a (i.e., between rear wall 27 of housing 20 and arms 16 and 16a). Cylinder 35 is held therein by the inner walls of housing 20 and arms 16 and 16a and thus is as long as the spacing between side rail 33 and side wall 32 of housing 20. That is, the diameter of cylinder 35 is related to the space formed within housing 20 between arms 16 and 16a, rear wall 27 and top and bottom walls 25 and 26, as can clearly be seen in FIG. 3. The rear portions 37 of arms 16 and 16a are cut out as shown (see also FIGS. 4 and 5). That is, portions 37 may be arcuate with the radius of the arcs forming portions 37 being slightly greater than the radius of cylinder 35. Thus, a gap as shown in FIG. 3 is preferably formed between portions 37 and the periphery of cylinder 35 as the portions 37 encircle the periphery thereof so that the arms 16 and 16a can easily move about cylinder 35 to compress cylinder 35. However, the junction of portions 37 with the elongated sides of arms 16 and 16a form upper and lower lips 39 and 40 or the like. These lips 39 and 40 compress against cylinder 35 at their points of engagement and form a generally airtight seal with cylinder 35 and the inner walls of housing 20. This seal is furthered by the fact that the material for cylinder 35 is selected to provide a material having flow characteristics so that in effect it is deformed and flows against the inner walls of housing 20. A suitable material would be 58 Durometer rubber. Thus, since it is not exposed to the atmosphere, the useful life thereof is greatly prolonged.

Although member 35 has been described as cylindrical, it may be generally or nearly so, such as octagonshaped, as long as it accomplishes the objectives of my invention. Further, it may be solid with an axial hole, if desired. This is shown in FIG. 8 where cylinder 35a has an axial hole 36. The diameter of the axial hole 36' may be varied as shown, if desired, to thus vary the strength and flow characteristics of the cylinder 35a. It can be seen, therefore, that both cylinders 35 and 35a act similar to hydraulic fluid. They may be readily and easily preloaded as desired by varying the shape of the opening or slots 29 in arms 16 and 16a.

The arms 16 and 16a are shown more particularly in FIGS. 4 and 5, respectively. The arm 16 is referred to as the internal or inboard arm and arm 16a as the outside or outboard arm. The configuration of the cut-out ends 37 of arms 16 and 16a and their midportions are identical. The lower edges of arms 16 and 16a each include a stop member 38 for engaging the bottom wall 26 of housing 20. The lips 39 and 40 are formed by chamfering the elongated edges of arms 16 and 16a at an angle of about 45 outwardly therefrom (e.g., for about 3/16 X 1% inches at the top and for about /4 X 3 /2 inches at the bottom). Any suitable material may be used for forming arms 16 and 16a, such as lA-inch hot rolled low-carbon steel plate. Finally, the ends 41 and 42 of arms 16 and 16a, respectively, may be flared upwardly and outwardly as shown. End 42 is so flared so that when arm 16 swings all the way up, it will be above the bottom of fixed platform 11 and stopped by the upper surface 25 of housing 20. End 41 is so flared so that arm 16a does not fall below the bottom of platform 11 and snag underneath.

In operation, ramp may be placed in bridging relationship to platforms 11 and 12 entirely by means of a forklift truck. Moreover, since the ramp l0 possesses a self-locking character, no manual effort is required. The ramp may be located in bridging relationship by either sliding the ramp from platform 11 toward platform 12, or it may be positioned entirely by vertical placement.

It will be apparent that as ramp 10 is either lowered into position or moved along platform 11 toward platform 12, arms 16 and 16a drop off of platform 11 and behind the abutment 17 (FIG. 2). The tooth l9 closest to abutment 17 will, of course, determine the limit to which ramp 10 can be moved in the direction of ramp l1, and when the step surface 14 of ramp 10 engages shoulder of platform 12, the ramp becomes locked in a spanning relationship to platforms 11 and 12 with supporting members 28 resting on platform 12.

It can be seen from the foregoing description that a positive resilient action takes place throughout the entire distance between the individual teeth 19 and the cylinder 35. Prior to loading platform 12, as shown in FIG. 6, the upper surface of body portion 13 of ramp 10 is generally planar and flush to the upper surface of platform 12. As the railroad car 12 becomes loaded, platform 12 moves downwardly as indicated by arrow 43 and the dotted lines in FIG. 7 until a slight angle is formed between these surfaces. However, as can be seen, the positive resilient action of arms 16 and 16a and cylinder 35 prevents any appreciable gap from forming between these surfaces, and the edges thereof are still generally flush and the upper surfaces are still generally planar.

The members 28 (FIG. 1) support ramp 10 in a manner that takes up little if any loading space within railroad car 12'. The cylinder 35 is completely sealed and protected within the housing 20. All of the joints of the walls forming housing 20 and its connection on ramp 10 are preferably welded for reasons of strength (since the ramp 10 is subject to tremendous stresses) and for smoothness of the contours and surfaces of ramp 10. Thus, since access to the interior of housing 20 is impossible after welding, the reason for protecting cylinder 35 from environmental damage (thus necessitating replacement) becomes evident.

The preloading of cylinder 35 is accomplished by moving the arms 16 and 16a to the upright position along slots 29, then pressing downwardly to press lips 40 into cylinder 35 to stress it. It would be extremely difficult to preload cylinder 35 without such an arrangement.

I claim as my invention:

1. A ramp adapted to bridge a pair of spaced platforms, one of said platforms being fixed and the other being movable, said ramp comprising:

a stepped undersurface at one end adapted to engage the edge of said movable platform while the other end of said ramp is adapted to be supported on said fixed platform; and

first ramp biasing means associated with said ramp for biasing said ramp in a plurality of differing selflocking positions between said platforms, said ramp biasing means including a housing mounted on one side of said ramp, said housing having a rear wall and a top and bottom wall forming upper and lower surfaces, respectively, and being open toward the endof said ramp which is adapted to be supported on said fixed platform, at least a pair of elongated arms pivotally connected at one end within said housing vertically movable about a common horizontal axis extending generally transversely of said ramp, said arms being of differing lengths and extending out of the open end of the housing, the vertical movement of said arms being limited by their selective engagement with the upper and lower surfaces of said housing, said arms each having a plurality of downwardly extending teeth on the free ends thereof adapted to extend below the undersurface of said ramp when the arms pivot vertically downwardly into engagement with the lower surface of said housing, said teeth also varying in overall distance from said common horizontal axis, and a generally cylindrical rubberlike member disposed within said housing between said common horizontal axis and the rear wall of said housing, said cylindrical member having its longitudinal axis extending generally transverse to said ramp and generally parallel and spaced from said common horizontal axis, and said member being in contiguous relationship with the rear ends of said arms, the inner walls of both said upper and lower surfaces and said rear wall.

2. The ramp of claim 1 wherein said teeth are tapered downwardly.

3. The ramp of claim 1 wherein a second ramp biasing means are associated with said ramp for biasing said ramp in a plurality of differing self-locking positions between said platforms, said ramp biasing means including a second housing mounted on the other side of said ramp, said second housing having a rear wall and a top and bottom wall forming upper and lower surfaces, respectively, and being open toward the end of said ramp which is adapted to be supported on said fixed platform, at least a pair of elongated arms pivotally connected at one end within said second housing vertically movable about a common horizontal axis extending generally transversely of said ramp, said arms being of differing lengths and extending out of the open end of the second housing, the vertical movement of said arms being limited by their selective engagement with the upper and lower surfaces of said second housing, said arms each having a plurality of downwardly extending teeth on the free ends thereof adapted to extend below the undersurface of said ramp when the arms pivot vertically downwardly into engagement with the lower surface of said second housing, said teeth also varying in overall distance from said common horizontal axis, and a generally cylindrical rubberlike member disposed within said second housing between said common horizontal axis and the rear wall of said second housing, said cylindrical member having its longitudinal axis extending generally transverse to said ramp and generally parallel and spaced from said common horizontal axis, and said member being in contiguous relationship with the rear ends of said arms, the inner walls of both said upper and lower surfaces and said rear wall.

4. The ramp of claim 1 wherein said housing is welded onto said ramp in a manner wherein the upper surfaces of said housing are generally flush with the upper surfaces of said ramp.

5. The ramp of claim 1 wherein said cylindrical member includes an axial hole therethrough varying in diameter throughout its length.

6. The ramp of claim 1 wherein said arms include stop means on the lower surfaces thereof adapted to contact the lower surface of said housing when pivoted downwardly.

7. The ramp of claim 1 wherein the upper surface of said ramp is generally flush with the upper surface of said movable platform when said ramp bridges the spacing between said platform.

8. The ramp of claim 1 wherein each of said arms includes a generally rectangular opening therein surrounding said common horizontal axis, said opening permitting each of said arms to pivot about said horizontal axis and each of said openings having means associated therewith for shifting said arms in a direction generally parallel to said ramp to thereby compress said cylindrical member.

9. The ramp of claim 8 wherein the ends of said arms contiguous to said member are cut out and surround said member along at least a portion of the periphery thereof, each of said cut-out portions including upper and lower chamfered portions engaging spaced portions on the periphery of said member at the upper and lower limits of the contact of said cut-out portions with said member.

10. The ramp of claim 9 wherein said arms are in a noncontiguous relationship with said member along said cut-out portions between said upper and lower chamfered portions.

11. Apparatus for bridging the space between a pair of platforms, one of said platforms being fixed and the other being movable, said apparatus comprising:

a ramp having a stepped undersurface at one end engaging the edge of said movable platform while the other end of said ramp is supported on said fixed platform; and

ramp biasing means associated with said ramp biasing said ramp in a self-locking position between said platforms, said ramp biasing means including a housing mounted on one side of said ramp, said housing having a rear wall and a top and bottom wall forming upper and lower surfaces, respectively, and being open toward the end of said ramp which is supported on said fixed platform, at least a pair of elongated arms pivotally connected at one end within said housing vertically movable about a common horizontal axis extending generally transversely of said ramp, said arms being of differing lengths and extending out of the open end of the housing, the vertical movement of said arms being limited by their selective engagement with the upper and lower surfaces of said housing, said arms each having a plurality of downwardly extending teeth on the free ends thereof with at least one of said teeth extending below the undersurface of said ramp when the arms are pivoted vertically downwardly into engagement with the lower surface of said housing, said teeth also varying in overall distance from said common horizontal axis, and a generally cylindrical rubberlike member disposed within said housing between said common horizontal axis and the rear wall of said housing, said cylindrical member having its longitudinal axis extending generally transverse to said ramp and generally parallel and spaced from said common horizontal axis, and said member being in contiguous relationship with the rear ends of said arms, the inner walls of both said upper and lower surfaces and said rear wall. 

1. A ramp adapted to bridge a pair of spaced platforms, one of said platforms being fixed and the other being movable, said ramp comprising: a stepped undersurface at one end adapted to engage the edge of said movable platform while the other end of said ramp is adapted to be supported on said fixed platform; and first ramp biasing means associated with said ramp for biasing said ramp in a plurality of differing self-locking positions between said platforms, said ramp biasing means including a housing mounted on one side of said ramp, said housing having a rear wall and a top and bottom wall forming upper and lower surfaces, respectively, and being open toward the end of said ramp which is adapted to be supported on said fixed platform, at least a pair of elongated arms pivotally connected at one end within said housing vertically movable about a common horizontal axis extending generally transversely of said ramp, said arms being of differing lengths and extending out of the open end of the housing, the vertical movement of said arms being limited by their selective engagement with the upper and lower surfaces of said housing, said arms each having a plurality of downwardly extending teeth on the free ends thereof adapted to extend below the undersurface of said ramp when the arms pivot vertically downwardly into engagement with the lower surface of said housing, said teeth also varying in overall distance from said common horizontal axis, and a generally cylindrical rubberlike member disposed within said housing between said common horizontal axis and the rear wall of said housing, said cylindrical member having its longitudinal axis extending generally transverse to said ramp and generally parallel and spaced from said common horizontal axis, and said member being in contiguous relationship with the rear ends of said arms, the inner walls of both said upper and lower surfaces and said rear wall.
 2. The ramp of claim 1 wherein said teeth are tapered downwardly.
 3. The ramp of claim 1 wherein a second ramp biasing means are associated with said ramp for biasing said ramp in a plurality of differing self-locking positions between said platforms, said ramp biasing means including a second housing mounted on the other side of said ramp, said second housing having a rear wall and a top and bottom wall forming upper and lower surfaces, respectively, and being open toward the end of said ramp which is adapted to be supported on said fixed platform, at least a pair of elongated arms pivotally connected at one end within said second housing vertically movable about a common horizontal axis extending generally transversely of said ramp, said arms being of differing lengths and extending out of the open end of the second housing, the vertical movement of said arms being limited by their selective engagement with the upper and lower surfaces of said second housing, said arms each having a plurality of downwardly extending teeth on the free ends thereof adapted to extend below the undersurface of said ramp when the arms pivot vertically downwardly into engagement with the lower surface of said second housing, said teeth also varying in overall distance from said common horizontal axis, and a generally cylindrical rubberlike member disposed within said second housing between said common horizontal axis and the rear wall of said second housing, said cylindrical member having its longitudinal axis extending generally transverse to said ramp and generally parallel and spaced from said common horizontal axis, and said member being in contiguous relationship with the rear ends of said arms, the inner walls of both said upper and lower surfaces and said rear wall.
 4. The ramp of claim 1 wherein said housing is welded onto said ramp in a manner wherein the upper surfaces of said housing are generally flush with the upper surfaces of said ramp.
 5. The ramp of claim 1 wherein said cylindrical member includes an axial hole therethrough varying iN diameter throughout its length.
 6. The ramp of claim 1 wherein said arms include stop means on the lower surfaces thereof adapted to contact the lower surface of said housing when pivoted downwardly.
 7. The ramp of claim 1 wherein the upper surface of said ramp is generally flush with the upper surface of said movable platform when said ramp bridges the spacing between said platform.
 8. The ramp of claim 1 wherein each of said arms includes a generally rectangular opening therein surrounding said common horizontal axis, said opening permitting each of said arms to pivot about said horizontal axis and each of said openings having means associated therewith for shifting said arms in a direction generally parallel to said ramp to thereby compress said cylindrical member.
 9. The ramp of claim 8 wherein the ends of said arms contiguous to said member are cut out and surround said member along at least a portion of the periphery thereof, each of said cut-out portions including upper and lower chamfered portions engaging spaced portions on the periphery of said member at the upper and lower limits of the contact of said cut-out portions with said member.
 10. The ramp of claim 9 wherein said arms are in a noncontiguous relationship with said member along said cut-out portions between said upper and lower chamfered portions.
 11. Apparatus for bridging the space between a pair of platforms, one of said platforms being fixed and the other being movable, said apparatus comprising: a ramp having a stepped undersurface at one end engaging the edge of said movable platform while the other end of said ramp is supported on said fixed platform; and ramp biasing means associated with said ramp biasing said ramp in a self-locking position between said platforms, said ramp biasing means including a housing mounted on one side of said ramp, said housing having a rear wall and a top and bottom wall forming upper and lower surfaces, respectively, and being open toward the end of said ramp which is supported on said fixed platform, at least a pair of elongated arms pivotally connected at one end within said housing vertically movable about a common horizontal axis extending generally transversely of said ramp, said arms being of differing lengths and extending out of the open end of the housing, the vertical movement of said arms being limited by their selective engagement with the upper and lower surfaces of said housing, said arms each having a plurality of downwardly extending teeth on the free ends thereof with at least one of said teeth extending below the undersurface of said ramp when the arms are pivoted vertically downwardly into engagement with the lower surface of said housing, said teeth also varying in overall distance from said common horizontal axis, and a generally cylindrical rubberlike member disposed within said housing between said common horizontal axis and the rear wall of said housing, said cylindrical member having its longitudinal axis extending generally transverse to said ramp and generally parallel and spaced from said common horizontal axis, and said member being in contiguous relationship with the rear ends of said arms, the inner walls of both said upper and lower surfaces and said rear wall. 